As described by Sullivan & Lynch in U.S. Pat. No. 5,199,424, issued on Apr. 6, 1993, the application of continuous positive airway pressure (CPAP) has been used as a means of treating the occurrence of obstructive sleep apnea. The patient is connected to a positive pressure air supply by means of a nose mask or nasal prongs. The air supply breathed by the patient is slightly greater than atmospheric pressure. It has been found that the application of continuous positive airway pressure provides what can be described as a “pneumatic splint”, supporting and stabilizing the upper airway and thus eliminating the occurrence of upper airway occlusions. It is effective in eliminating both snoring and, obstructive sleep apnea and in many cases, is effective in treating central and mixed apnea.
In U.S. Pat. No. 5,549,106 to Gruenke, issued on Aug. 27, 1996, an apparatus is disclosed that is intended for facilitating the respiration of a patient for treating mixed and obstructive sleep apnea. The device is said to increase nasal air pressure delivered to the patient's respiratory passages just prior to inhalation and by subsequently decreasing the pressure is said to ease exhalation effort.
In U.S. Pat. No. 5,245,995 Sullivan discusses how snoring and abnormal breathing patterns can be detected by inspiration and expiration pressure measurements while sleeping, thereby leading to early indication of preobstructive episodes or other forms of breathing disorder. Particularly, patterns of respiratory parameters are monitored, and CPAP pressure is raised on the detection of pre-defined patterns to provide increased airway pressure to, ideally, subvert the occurrence of the obstructive episodes and the other forms of breathing disorder.
As described by Berthon-Jones in U.S. Pat. No. 5,704,345, issued on Jan. 6, 1998, various techniques are known for sensing and detecting abnormal breathing patterns indicative of obstructed breathing, the disclosures of which are incorporated herein by reference. Berthon-Jones describes methods based on detecting events such as apnea, snoring, and respiratory flow limitation, e.g. flattening of the inspiratory portion of a flow curve. Treatment pressure may be automatically adjusted in response to the detected conditions. Berthon-Jones also describes methods for detecting central apneas.
Other methods for detecting obstruction have also been used. For example, in. U.S. Pat. Nos. 5,490,502 and 5,803,066, Rapoport is said to disclose a method and apparatus for optimizing the controlled positive pressure to minimize the flow of air from a flow generator while attempting to ensure that flow limitation in the patient's airway does not occur. Controlled positive pressure to the airway of a patient is said to be adjusted by detecting flow limitation from the shape of an inspiratory flow waveform. The CPAP pressure setting is raised, lowered or maintained depending on whether flow limitation has been detected and on the previous actions taken by the system.
In U.S. Pat. No. 5,645,053, Remmers is said to describe a system for automatically and continuously regulating the level of nasal pressure to an optimal value during OSA (Obstructive Sleep Apnea) treatment. Parameters related to the shape of a time profile of inspiratory flow are determined including a degree of roundness and flatness of the inspiratory profile. OSA therapy is then implemented by automatically re-evaluating an applied pressure and continually searching for a minimum pressure required to adequately distend a patient's pharyngeal airway.
Another type of device for treating sleep disordered breathing is the device disclosed by Farrugia and Alder in International Patent Application No. PCT/US2004019598 (Publ. No. WO 2004/112680) and corresponding U.S. Pat. No. 7,128,069, the disclosure of which is incorporated herein by reference. A CPAP pressure that is delivered to the patient may be adjusted to treat sleep disordered breathing events such as detected partial or complete obstruction. The delivered pressure may be slightly reduced from the set CPAP pressure upon detection of patient expiration. This expiratory pressure relief (EPR) can provide comfort for the patient while the patient exhales since it may be easier to exhale at the reduced pressure when compared to the higher CPAP pressure. The delivered pressure is then returned to the set CPAP pressure upon detection of patient inspiration.
Despite the availability of such devices for treating OSA, some sleep disordered breathing events may still go untreated with the use of some devices. Thus, it will be appreciated that there may be a need for improved techniques and devices for addressing the conditions of sleep disordered breathing while balancing the desire for patient comfort.